In the field of audio engineering, digital technology has been used most often in the design of professional equipment. Recently, consumer video cassette tape recorders have incorporated digital technology and movement toward using digital data in consumer audio equipment appears to be accelerating.
A major reason for this trend is that the PCM recording and playback system, which is made possible by combining a video tape recorder (VTR) and digital technology, has a much broader dynamic range than do conventional analog tape recorders. Another reason is that in comparison with those conventional recorders, the PCM system has practically no wow and flutter. Also, the PCM systems' frequency and distortion characteristics are substantially superior to those of analog systems.
A PCM audio system connected to a VTR requires a digital signal processor to transform the PCM signal format to and from the appropriate television signal format. The format of the PCM audio signal may be the one prescribed by the EIAJ (Electronic Industries Association of Japan) Technical File: STC-007, which employs bit error correction schemes together with interleaving techniques. This format will be described in detail below.
The PCM audio signals are encoded in the EIAJ format for the VTR by delaying the interleaving of the data words and by adding both an error correction check word and an error detection check word. Conventional PCM signal processors for decoding the encoded PCM audio signals include de-interleave circuits which contain several error pointer signals for error detection and correction. The error pointer signals are given different amounts of delay by branching an original error pointer signal through parallel delay lines of the de-interleave circuits.
One major problem with the prior art PCM decoders is that the error correction mechanism malfunctions every time there is an erroneous error pointer signal.